Re: [PATCH 02/13] kprobe: Keep traced function address

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Jan 05, 2022 at 11:32:52PM +0900, Masami Hiramatsu wrote:
> On Tue,  4 Jan 2022 09:09:32 +0100
> Jiri Olsa <jolsa@redhat.com> wrote:
> 
> > The bpf_get_func_ip_kprobe helper should return traced function
> > address, but it's doing so only for kprobes that are placed on
> > the function entry.
> > 
> > If kprobe is placed within the function, bpf_get_func_ip_kprobe
> > returns that address instead of function entry.
> > 
> > Storing the function entry directly in kprobe object, so it could
> > be used in bpf_get_func_ip_kprobe helper.
> 
> Hmm, please do this in bpf side, which should have some data structure
> around the kprobe itself. Do not add this "specialized" field to
> the kprobe data structure.

ok, will check

thanks,
jirka

> 
> Thank you,
> 
> > 
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  include/linux/kprobes.h                              |  3 +++
> >  kernel/kprobes.c                                     | 12 ++++++++++++
> >  kernel/trace/bpf_trace.c                             |  2 +-
> >  tools/testing/selftests/bpf/progs/get_func_ip_test.c |  4 ++--
> >  4 files changed, 18 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> > index 8c8f7a4d93af..a204df4fef96 100644
> > --- a/include/linux/kprobes.h
> > +++ b/include/linux/kprobes.h
> > @@ -74,6 +74,9 @@ struct kprobe {
> >  	/* Offset into the symbol */
> >  	unsigned int offset;
> >  
> > +	/* traced function address */
> > +	unsigned long func_addr;
> > +
> >  	/* Called before addr is executed. */
> >  	kprobe_pre_handler_t pre_handler;
> >  
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index d20ae8232835..c4060a8da050 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1310,6 +1310,7 @@ static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
> >  	copy_kprobe(p, ap);
> >  	flush_insn_slot(ap);
> >  	ap->addr = p->addr;
> > +	ap->func_addr = p->func_addr;
> >  	ap->flags = p->flags & ~KPROBE_FLAG_OPTIMIZED;
> >  	ap->pre_handler = aggr_pre_handler;
> >  	/* We don't care the kprobe which has gone. */
> > @@ -1588,6 +1589,16 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >  	return ret;
> >  }
> >  
> > +static unsigned long resolve_func_addr(kprobe_opcode_t *addr)
> > +{
> > +	char str[KSYM_SYMBOL_LEN];
> > +	unsigned long offset;
> > +
> > +	if (kallsyms_lookup((unsigned long) addr, NULL, &offset, NULL, str))
> > +		return (unsigned long) addr - offset;
> > +	return 0;
> > +}
> > +
> >  int register_kprobe(struct kprobe *p)
> >  {
> >  	int ret;
> > @@ -1600,6 +1611,7 @@ int register_kprobe(struct kprobe *p)
> >  	if (IS_ERR(addr))
> >  		return PTR_ERR(addr);
> >  	p->addr = addr;
> > +	p->func_addr = resolve_func_addr(addr);
> >  
> >  	ret = warn_kprobe_rereg(p);
> >  	if (ret)
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 21aa30644219..25631253084a 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1026,7 +1026,7 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> >  {
> >  	struct kprobe *kp = kprobe_running();
> >  
> > -	return kp ? (uintptr_t)kp->addr : 0;
> > +	return kp ? (uintptr_t)kp->func_addr : 0;
> >  }
> >  
> >  static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
> > diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > index a587aeca5ae0..e988aefa567e 100644
> > --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > @@ -69,7 +69,7 @@ int test6(struct pt_regs *ctx)
> >  {
> >  	__u64 addr = bpf_get_func_ip(ctx);
> >  
> > -	test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
> > +	test6_result = (const void *) addr == &bpf_fentry_test6;
> >  	return 0;
> >  }
> >  
> > @@ -79,6 +79,6 @@ int test7(struct pt_regs *ctx)
> >  {
> >  	__u64 addr = bpf_get_func_ip(ctx);
> >  
> > -	test7_result = (const void *) addr == &bpf_fentry_test7 + 5;
> > +	test7_result = (const void *) addr == &bpf_fentry_test7;
> >  	return 0;
> >  }
> > -- 
> > 2.33.1
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@kernel.org>
>